Panasonic sc tnpa5081 rebuild

[tw2005]

I've got 3 of these boards now and had no luck finding somone with a good one so I'm biting the bullet and going to have a go at component level.

I've worked out most of what i think is failed when I stumbled across a reading across the 5v reg IC16771 VAD +5V between gnd and out of 5.2ohms. The other 2 boards have 2 & 8 ohms.

This seems too low and would exceed what the little reg would handle I believe.

Through elimination I've tracked it to what I believe is a 5pin, 2 input NAND gate. It has a marking "HA" which I believe I've tracked down as a 74HC1G00GW, SOT353 .

I've confirmed out of cct the resistance between gnd and Vcc to the same 5.2 ohms and there is no longer that resistance present on the 5v reg.

Just looking for advice or confirmation of my findings. Does anyone know what you'd expect to see across the nand gnd/Vcc?

If I do get lucky and get one going I'll be adding all my research down the track.

The pictures are one out of the manual & the other is from the datasheet for what I believe this is.

[tom66]

Re: Panasonic sc tnpa5081 rebuild

You'd expect to see more than a kohm between Vcc and GND so it's definitely bad. Question is why did it go bad. A logic gate is pretty reliable. Perhaps something on what it is connected to shorted to a higher voltage like Vsus.

[tw2005]

Re: Panasonic sc tnpa5081 rebuild

You'd expect to see more than a kohm between Vcc and GND so it's definitely bad. Question is why did it go bad. A logic gate is pretty reliable. Perhaps something on what it is connected to shorted to a higher voltage like Vsus.

Yeah it's the needle in the haystack Tom. SU board short on 5V line, and another(i forget Vfo) and a dead SC.

RJP63F3A x 1
30F125 x 2
178M05 x 1
DG502LWx2
DG402RP x 2
45G128 x 1
M81737FP x 1

Oh and this is the "Tested Working " board I was supplied. I know, I'm dreaming like you said about these being tested.

It won't be a cheap gamble to see if I get it going. I just wish i still had my good spare to compare the pair.

I just found another nand onboard(smaller too! ) it tests in the K ohms about 4.

Am I correct about what this device is?

[tw2005]

Re: Panasonic sc tnpa5081 rebuild

May have jumped to a conclusion too soon. just looked at some inverter cmos logic chips at RS and they have the exact pinouts. I was thinking they labelled NC as it was not used(pin 1) But the case is marked HA?

[tom66]

Re: Panasonic sc tnpa5081 rebuild

It's an inverter, not a NAND. Something like 74LVC1G04.

[tw2005]

Re: Panasonic sc tnpa5081 rebuild

It's an inverter, not a NAND. Something like 74LVC1G04.

Cheers, I'm leaning that way too although no idea what spec. I'll check it out.

[tw2005]

Re: Panasonic sc tnpa5081 rebuild

Ok I've found this on only one board shorted. D16790 markings 34 and I think it might be this diode pd3s120l,

What do you think? Is this simply cct protection? The way I see it if it was removed the cct would work.

The dimensions and ratings make it conceiveable it's correct.


Edit: after a closer look this is also part of the 15V fed to IC16521 FET driver M81737FP, 6.2 ohms across the diode and Vcc/gnd at the chip which are all in cct. I think it's going to be the IC.

[tw2005]

Re: Panasonic sc tnpa5081 rebuild

here's some buffer boards measurements I have on 3 sets.

[tom66]

Re: Panasonic sc tnpa5081 rebuild

Looks like a transorb (TVS) to absorb spikes on 15V line.

[tw2005]

Re: Panasonic sc tnpa5081 rebuild

Looks like a transorb (TVS) to absorb spikes on 15V line.

Transorb? man, I am out of touch. Did you have a look at those readings in my spreadsheet?

Is it the same schematic symbol for a TVS as for a diode?

[tom66]

Re: Panasonic sc tnpa5081 rebuild

TVS is basically a diode that "normally" never conducts. It can handle large reverse power of up to 5000W peak (around 500W for an SMD one.) Basically shorts out the supply if there's a failure. Think of it as a high power zener diode.

[tw2005]

Re: Panasonic sc tnpa5081 rebuild

Just spotted another small difference in the boards. Rev AF,AP have no capacitor installed at C461 (C16461), AW does. What's interesting here is in my manual which has the AF rev, it shows it in cct and on the parts list. This may explain why the same part number is showing for Q660 & Q601 which are both RJP6026 transistors on the AW and on the AF,AP R5007ANX transistors at Q660 and at Q601 it's RJP6026.

[tw2005]

Re: Panasonic sc tnpa5081 rebuild

Ok I've found this on only one board shorted. D16790 markings 34 and I think it might be this diode pd3s120l,

What do you think? Is this simply cct protection? The way I see it if it was removed the cct would work.

The dimensions and ratings make it conceiveable it's correct.


Edit: after a closer look this is also part of the 15V fed to IC16521 FET driver M81737FP, 6.2 ohms across the diode and Vcc/gnd at the chip which are all in cct. I think it's going to be the IC.

Confirmed, IC16521 short or 6.2ohms across gnd/vcc. Diode now checks ok.

[tw2005]

Re: Panasonic sc tnpa5081 rebuild

It's an inverter, not a NAND. Something like 74LVC1G04.

Tom, I ordered that 74LVC1G04 from RS and arrived today but last night I believe I found the correct item.

Toshiba TC7SH14F, marking HA, Schmitt NOT

http://home.zcu.cz/~ronesova/index.p...uitem=tos1gate

I think the 74LVC1G04 should still do the job or should I try and get the Toshiba which are out of stock at RS until early march.


Any thoughts?

[tom66]

Re: Panasonic sc tnpa5081 rebuild

The normal inverter doesn't have Schmitt tendencies, so it might pick up more noise. I would suggest a Schmitt substitute.

[tw2005]

Re: Panasonic sc tnpa5081 rebuild

The normal inverter doesn't have Schmitt tendencies, so it might pick up more noise. I would suggest a Schmitt substitute.

Good pickup, was not even looking for that. Just the basic stuff like voltage,current ratings and propagation delay not that I really know what the hell I should be focussing on.

So this one came up using Ti cross reference.

SN74AHCG14

So the really hard question, using non schmitt will it;
a.work
b.not work
c. smoke
d. No idea, take my advice and get the right one

[tom66]

Re: Panasonic sc tnpa5081 rebuild

D. I'm going to go with "D".

[tw2005]

Re: Panasonic sc tnpa5081 rebuild

LOL. I would too, oh well who said progress was always easy.

At least I've finally found the right device, brand and markings. It was bugging me taking a pot shot.

[rcpilot82]

Re: Panasonic sc tnpa5081 rebuild

Have you found a source for this part yet? M81737FP

I know I have a blown one on my board and I could not source one.

[tw2005]

Re: Panasonic sc tnpa5081 rebuild

If anything you should be able to get any part direct from the several suppliers of OEM TV parts in your country.

How hard are you trying? Have you downloaded a manual yet as all the part numbers are in that.

I can't as none will deal out of the US.

http://cceparts.com/productdetail.as...r=C0ZBZ0001708

http://www.searspartsdirect.com/part...01708/0057/528

Have you had a chance to resistance test those buffer boards of yours and post the results for me to compare?